The present invention relates to a conductive polymer actuator having rigidity in contraction direction and driving force in expansion direction and to a robot using the same.
With increased demands for machines operating in places near human beings such as household robots, expectation for artificial muscle actuators with smooth operation like human muscles are growing. Various types of actuator have been proposed as candidates of the artificial muscle actuator, and among these is an actuator using conductive polymer.
As one example of the artificial muscle actuators using conductive polymer, an actuator for generating bending deformation as shown in FIG. 11A, FIG. 11B, and FIG. 11C has been proposed. The actuator is structured to hold a solid electrolyte compact 22 between polyaniline film members 21a and 21b which are conductive polymer films. When a switch 98 is turned on, potential difference set in a power source 97 is applied to between the polyaniline film members 21a and 21b, so that as shown in FIG. 11B, anions are inserted into one polyaniline film member 21b to expand the polyaniline film member 21b, while anions withdraw from the other polyaniline film member 21a to compress the polyaniline film member 21a, resulting in generation of the bending deformation (see, e.g., Patent Document 1: Japanese Unexamined Patent Publication No. H11-169393).
While in this structure, the bending deformation is generated by difference in displacement magnitude between two conductive polymer films acting as electrodes, in another structure, there is known an actuator in which an electrolyte holding layer is made from liquid or gel materials so as to prevent deformation of both electrodes from influencing each other, and displacements of only one conductive polymer are extracted for expansion and contraction deformation. In this case, the electrode which does not utilize displacements does not need to be a conductive polymer and therefore a metal electrode is mainly used, and further it is indicated that providing conductive polymer on the metal electrode increases displacements (see Non-Patent Document 1: Proceedings of SPIE, Vol. 4695, pages 8 to 16).
Since this kind of conductive polymer actuator generates a strain equal to that of muscles at a low voltage of 2 to 3 V, its practical application as an artificial muscle is expected.
However, in the case of using conductive polymer as an actuator for performing expansion and contraction deformation, it is impossible for the conductive polymer as it is to have driving force in its expansion direction or rigidity in its contraction direction because the conductive polymer is in a film state. To solve this issue, a method for generating driving force and rigidity to both the directions by applying preloads by springs to an expansion direction of a conductive polymer film is shown in Non-Patent Document 1 (Proceedings of SPIE, Vol. 4695, pages 8 to 16). Moreover, a method for obtaining the same effects by applying preloads by weights is shown in Non-Patent Document 2 (Japanese Journal of Applied Physics, Vol. 41, Part 1, No. 12, Page 7532 to 7536).
However, the actuators having the above structures for performing expansion and contraction deformation still have issues. In the structure involving application of preloads by springs, a spring having high rigidity is necessary for obtaining sufficient rigidity and driving force and in this case, displacements in its shrinkage direction are reduced.
In the structure involving application of preloads by weights, there are such issues that there is an influence in gravity direction, and also a mass of a weight affects dynamic characteristics.
An object of the present invention, in consideration of these issues, is to provide a conductive polymer actuator and a robot using the same capable of acquiring driving force in its expansion direction and rigidity in its contraction direction without the necessity of preloads.